Optical disks are an increasingly popular medium for digitally storing information. Optical disks are typically enclosed in box shaped disk cartridges having two notches formed near one end of the cartridge, with one notch located on each long side.
In some large-scale optical disk storage and retrieval systems, disks are stored in an array of storage slots, with each slot positioned vertically of the other slots to form a column. The storage systems often have several such columns arranged laterally of each other to form a two dimensional array of slots. The systems include disk retrieval mechanisms which use gripping means to retrieve a selected cartridge from its storage slot, transfer the cartridge to a disk reader, and to subsequently return the cartridge to its slot when instructed to do so. The gripping means normally grips the cartridge by engaging with the notches located on the side of the cartridge.
One necessary feature in the design of cartridge retrieval and return systems is a gripping means that is convertible between a retrieval mode, in which the gripping means is capable of engaging and carrying a disk cartridge, and a return mode in which the gripping means releases the disk cartridge so that it may be returned to its storage location. One presently available cartridge retrieval mechanism, described in U.S. Pat. No. 5,014,255, utilizes a pair of gripping arms proportioned for engaging the notches located on the sides of a disk cartridge. The gripping arms are pivotally mounted to a carriage which travels towards the disk cartridge. A spring biases the gripping arms inwardly such that when forward advancement of the carriage causes them to abut the end of a disk cartridge, the edges of the cartridge urge them laterally outward until they slip inwardly into engagement with the notches on the cartridge. The gripper arms and the carriage are disposed between a pair of rectangular plates which are connected at one end and which are proportioned to fit a retrieved cartridge between them.
A disadvantage with the currently available disk cartridge retrieval systems such as the one described above is that proper positioning of the gripper arms is conditioned upon proper positioning of guide members that move independently of the gripper arms. The change in position of the guide members that is needed to properly position the gripper arms is triggered by movement of the carriage and is only on the order of a few millimeters. Accurate positioning of each gripper arm is contingent upon successful travel of a small peg attached to that gripper arm through one of a series of narrow channels. Each peg is guided into the appropriate channel by proper positioning of one of the guide members. The device is thus highly tolerance-dependent, has an increased likelihood of malfunction caused by improper alignment of moving parts, and is expensive to construct in such a way as to achieve adequate precision.
Yet another disadvantage with currently available systems is that the components used for biasing the gripper arms are configured such that excessive force is exerted on the biasing spring when the gripper arm is pivoted laterally of the carriage during ejection of a cartridge. The force on the biasing spring increases well above the normal spring rate and thereby exposes the spring and other components to substantial forces that can precipitate premature wear.